The invention relates to the equipment for maintenance of mainlines, and more particularly, to a working tool of a machine for cleaning the outer surface of welded pipes from old artirust coating, rust and dirt.
It is known that antirust coating of operating mainlines is destroyed in time under the action of external factors (temperature differences, mechanical damages and the like). Pipe metal corrodes in the places of destruction of antirust coating so that even perforations of pipe walls may appear, especially in the zones of location of transverse welded joints of the pipeline due to differences between the weld metal and parent metal of the pipe, this action being much stronger in case of underground pipelines acted upon by soil electrolyte.
Service life of antirust coatings is considerably shorter than that of metal pipes so that it is necessary to of repair of antirust coatings at proper intervals.
The repair of mainlines, as a world-wide practice, is by replacing defective portions of pipeline by new ones. This requires suspension of product supply thus lowering the throughput capacity of the pipeline. It is therefore very important in the modern age to solve the problem of the overhaul of antirust coating of the outer surface of mainlines without interruption of product supply during the repair.
The invention may be most advantageously used for repair of operating mainlines of different diameters, in particular, gas and oil pipelines constructed of metal pipes welded-end-to-end.
Known machines for cleaning the outer surface of pipes of a mainline comprise a self-propelled carriage which is moved along the pipe being treated axially thereof during the cleaning and a working member mounted on the carriage which has a hollow casing accommodating an annular rotor co-axial with the pipe being treated which supports working tools.
Each working tool includes a tool holder in the form of a double-arm lever fixed to the rotor of the working member of the machine on the side of the pipe being treated for rotation in a plane extending at right angle to the pipe axis.
A tool is secured to the rear or trailing arm of the tool holder in the rotational direction of the rotor, and the front arm supports a counterweight for urging the tool against the surface of the pipe being treated during the cleaning under the action of centrifugal forces which are adjusted by the mass of the counterweight. The cutting edge of the tool in the prior art working tools extends, during the cleaning, in a plane tangential to the outer surface of the pipe being treated at an angle to the generatrix thereof.
Each working tool is provided with a cam for retracting the tool from the surface of the pipe being treated in the zones of location of projections thereof (welded joints, patches). The cam of prior art working tools comprises a plate bearing a cam and a support pivot arranged ahead of the tool in the rotational direction of the rotor. The plate is articulated to a pressure lever having an independent counterweight at the opposite end.
In the process of rotation of the rotor, the cam and the support pivot of the cam are urged against the surface of the pipeline by centrifugal forces developed at the counterweight. When the cam hits against a projection of the surface of the pipe being treated, such as against a welded joint, the plate rotates on the pivot relative to the articulation joint to cooperate with the tool holder arm so as to retract the tool from the welded joint thereby protecting the joint during cleaning. After the tool passes over the welded joint, the plate returns it back to the initial position.
The main disadvantage of the working tools of prior art machines for cleaning the outer surface of pipes resides in relatively complicated construction of the above-described cam which requires frequent adjustment and control of its cooperation with the tool under heavy dynamic and impact loads in the process of cleaning so as to avoid damages to the welded joints and to the surface of the pipe being treated. This results in frequent interruptions of the machine operation and lowers its productivity.